core: Add ruff rules PT (pytest) (#29381)

See https://docs.astral.sh/ruff/rules/#flake8-pytest-style-pt

libs/core/tests/unit_tests/messages/test_utils.py

@@ -1,5 +1,6 @@
 import base64
 import json
+import re
 import typing
 from collections.abc import Sequence
 from typing import Any, Callable, Optional, Union
@@ -513,7 +514,14 @@ def test_trim_messages_bound_model_token_counter() -> None:
 
 def test_trim_messages_bad_token_counter() -> None:
     trimmer = trim_messages(max_tokens=10, token_counter={})
-    with pytest.raises(ValueError):
+    with pytest.raises(
+        ValueError,
+        match=re.escape(
+            "'token_counter' expected to be a model that implements "
+            "'get_num_tokens_from_messages()' or a function. "
+            "Received object of type <class 'dict'>."
+        ),
+    ):
         trimmer.invoke([HumanMessage("foobar")])
 
 
@@ -852,7 +860,9 @@ def test_convert_to_messages_openai_refusal() -> None:
     assert actual == expected
 
     # Raises error if content is missing.
-    with pytest.raises(ValueError):
+    with pytest.raises(
+        ValueError, match="Message dict must contain 'role' and 'content' keys"
+    ):
         convert_to_messages([{"role": "assistant", "refusal": "9.1"}])